A simple and reasonably accurate method for the determination of low concs. of 2,4-dichlorophenoxyacetic acid is described in detail, the method being based on the rate of elongation of the primary root of germinated corn seedlings. The method is most accurate within concs. ranging from 0.1 to 1 ppm. The accuracy is lessened as the conc. increases or decreases, but higher concentrations can be tested readily by dilution to the more accurate levels. The entire procedure requires about 100 hrs. for completion.